Process for nitrosation of hydrocarbons



htates atent 3,32%,l43 Patented May 16, 1967 dice This invention relates to a photochemical process for the nitrosation of hydrocarbons, particularly of alkanes and cycloalkancs.

It is an object of the present invention to manufacture oximes having a given number of carbon atoms, by photochemical nitrosation of hydrocarbons having the same number of carbon atoms.

It is another object of this invention to manufacture addition salts of said oximes with acids.

It is still another object of this invention to manufac' ture said oximes and said salts thereof with a high yield, photochemically, and without substantial deposit of byproducts which reduce the light intensity throughout the reaction zone.

It is a further object of this invention to conduct the photochemical nitrosation of hydrocarbons in the liquid phase by means of irradiating lamps in such a manner as to avoid the necessity of periodically washing the lamps, which washing ordinarily requires the use of complex techniques.

These and other objects as may be apparent from the following specification and claims are achieved according to the present invention by passing in front of an actinic light source at an average linear velocity of at least 1 cm. per second, preferably of at least 3 cm. per second, and still more preferably in the range of about 4-50 cm. per second, a liquid phase containing the treated hydrocarbon having dissolved therein a nitrosating amount of a nitrosation agent at a maximum concentration of 5% by weight with respect to the treated hydrocarbon, the preferred range being about 0.l-2%.

According to a preferred embodiment of the process of this invention, the resulting reacted mixture is contacted with an aqueous solution of a strong mineral acid either inside or completely outside the irradiation zone, or both. Thereby, the hydrocarbon phase is stripped of the oxime or salts thereof by the strong mineral acid, and is then separated. The separated hydrocarbon phase is then recycled to the irradiation zone after, if necessary, replenishment with further amounts of nitrosation agent and hydrocarbon.

The solution of the oxime in the strong mineral acid may be neutralized in order to separate therefrom the oxirne or salts thereof. It may also be directly subjected to the Beckmann rearran ement by mere heating, where by the corresponding amide or lactame is obtained,

Although the excellent results achieved by the process of this invention have not yet been explained with complete satisfaction, it is assumed that the reaction occurs essentially in the zone where the reaction mixture contacts the transparent wall separating the mixture from the lamp and that the use of a high circulation velocity of the reactants in contact therewith provides for the mechanical carrying away of the conversion products prior to any possible further decomposition thereof to undesirable products.

Aside from merely the linear velocity as an important variable in this invention, the unexpectedly excellent results may result from the type of flow which in turn is dependent on the Reynolds Number for a given system.

The Reynolds Number is given by the formula:

4RI1G wherein Rh is the average hydraulic radius, i.e., in the case of a reaction vessel having an annular cross-section wherein D is the average external radius in centimeters of the reaction zone and d is the average internal radius in centimeters of the reaction zone;

G is the weight of reaction mixture flowing through the reaction zone per unit of time and of area, expressed in grams per sq. centimeter and per second; and

a is the viscosity of the reaction mixture, expressed in poises.

According to an embodiment of this invention, the Reynolds Number should preferably be higher than 1,000. the preferred values being comprised between 5,000 and 50,000.

The reaction product may be advantageously extracted substantially as it is formed and for example less than 1 minute and preferably less than 10 seconds after being withdrawn from the reaction zone.

The particular nitrosation agent of this invention is not of the essence thereof, but it is preferably a nitrosyl halide, particularly nitrosyi chloride, bromide or fluoride, although there may be used mixtures of halides with at least one nitrogen oxide such as nitric oxide, nitrous anhydride, or nitrogen peroxide. The nitrosyl halide may optionally be formed in situ by means of any convenient reaction therefor.

With respect to the preferred embodiments of this invention, the strong acid may be, for instance, from the group consisting of sulfuric acid, phosphoric acid, and hydrochloric acid.

lf sulfuric acid is employed, it has been discovered that the concentration of the aqueous sulfuric acid solution is highly important and has to be kept Within the range of from 50 to 90% by weight, and preferably between 60 and Otherwise, there will be a considerable decrease in the yield, particularly with respect to the nitrosation agent, and of the output capacity, as well as a rapid deactivation.

The same concentration range is also to be used with phosphoric acid; Whereas, in the case of the use of a hydrochloric acid solution, it must be as concentrated as possible, for example 30-40% by weight concentrated.

it has been also determined as a preferred characteristic of the present process that the step of contacting the reaction mixture with the strong mineral acid must be conducted outside of the irradiation zone, or substantially outside, i.e., at least in a zone where the irradiation intensity is very small as compared to that prevailing in the main irradiation Zone, and corresponds, for instance, to less than 10% of the latter.

The reaction is preferably carried out in the presence of a gaseous hydrogen halide, such as, for instance, hydrogen chloride. However, for the above-described preferred embodiment, such addition of gaseous halogen acid is unnecessary.

The strong acid is to be used in preferable amounts, for instance, of 0.1 to 10 mols per nitrogen atom of the oxime obtained. However, in order to carry out the Beckmann rearrangements, it is of advantage to employ at least one mol of acid per nitrogen atom present in the oxime obtained.

The reaction temperature will be advantageously kept in the range of from l0 to 40 C. and preferably be tween 5 and 15 C.

Although the liquid phase reaction mixture may consist only of the treated hydrocarbon together with the nitrosation agent, it may also contain a solvent substantially inert with respect to the nitrosation agent, particularly benzene, carbon tetrachloride or other chlorinated hydrocarbon solvents. The use of such a solvent is practically necessary where the treated hydrocarbons are normally in a solid state (case for instance of the cyclododecane) in order to avoid the use of excessively high reaction temperatures. However too dilute solutions of the hydrocarbon in the solvent, for example concentrations lower than 2% by weight, should preferably be avoided.

By actinic light there is meant radiant energy having a wave length lower than about 7,500 A. As source of actinic light there may be used, for instance, a mercury vapor lamp or a sodium vapor lamp. The preferred Wave length range is about 3,000-6,000 A.

This process, according to this invention, is applicable to alkanes and cycloalkanes, more particularly to the latter, and especially to those containing at least 5, and preferably from to 12 carbon atoms, such as heptane, cyclopentane, hexane, cyclohexane, octane, cyclooctane, dode-cane, and cyclododecane. It is to be understood, however, that this process is also applicable to alkanes and cycloalkanes having less than 5, and more than 12, carbon atoms.

The following comparative examples, which are not to be considered in any Way as limitative of the scope of this invention, are given only for the purpose of illustrating the advantages achievable by the process of this invention.

Example 1 There is used an apparatus comprising a central glass tube of a 70 cm. length having coaxially placed therein a tubular high pressure mercury vapor lamp of a 60 cm. useful length and a 2 kw. power. Cooling water is passed through said tube to prevent overheating.

The reaction mixture is circulated through a space formed between said tube and an external coaxial tube of a larger diameter, surrounding the same. The cross-section of pas-sage for the reaction mixture is bout 3 dm. the useful volume of the rection zone being about 18 liters.

At the outlet of the reaction zone, the reaction mixture is passed through a heat exchanger, and thereafter into a zone for absorption with 70% by weight sulfuric acid. After being separated and replenished with nitrosyl chloride, the hydrocarbon mixture is recycled to the inlet of the reaction zone by a pump.

The total capacity of the system is about 41 liters. There are initially introduced 40 liters of a mixture of cyclohexane with benzene having a 95% cyclohexane and a 5% benzene content, and to which is added 1% by weight of nitrosyl chloride, where as 1 liter of 70% by weight sulfuric acid is introduced into the absorption zone.

This mixture is circulated by means of a pump so as to obtain in the reaction zone an average linear velocity of 0.5 cm. per second which corresponds to anaverage residence time of the cyclohexane in the reaction zone of 120 seconds.

The Reynolds Number is about 1,500.

The lamp is then illuminated, and the temperature at the inlet of the reaction zone is maintained at about C.

After one hour, the sulfuric acid solution is withdrawn and neutralized at a temperature of C. by means of ammonia. The oxime is separated therefrom, dried and weighed. There are thus obtained 224 g. of cyclohexanone-oxime with a molar yield of 74.5% with respect to nitrosyl chloride, and 84% with respect to cyclohexane.

4 Example 2 Example 1 is repeated except that the average velocity of the reactants into the reaction zone is brought to 5 cm. per second, which corresponds to an average residence time of 12 seconds, the other conditions being unchanged. The Reynolds Number is about 15,000.

After one hour, the cyclohexanone-oxime yield is 332 g., an increase of 48% as compared to Example 1, which increased yield is clearly attributable to the increased linear velocity. The molar yields are 75.5%, with respect to nitrosyl chloride, and 84.5% with respect to cyclohexane.

Example 3 Example 2 is repeated except that the sulfuric acid solution is replaced by an aqueous solution of hydrochloric acid saturated at a temperature of 25 C.

The cyclohexanone-oxime production amounts to 325 g. after one hour. The molar yields are 74.9% wit-h respect to nitrosyl chloride and 84% with respect to cyclohexane.

Example 4 Example 2 is repeated, but in the absence of benzene. The cyclohexanone-oxime production amounts to 322 g. after one hour. The molar yields are 75.1% With respect to nitrosyl chloride and 85.2% with respect to cyclohexane.

Example 5 Example 2 is repeated, except that an average linear velocity of 1 cm. per second is employed. The cyclohexanone-oxime production amounts to 280 g. after one hours. The molar yields remain unchanged.

Example 6 Example 2 is repeated, except that an average linear velocity of 20 cm. per second is employed. The cyclohexanoneoxime production amounts to 340 g. after one hour. The molar yields are unchanged.

Example 7 There is used an irradiated vessel of annular cross-section having a useful volume of 2 l. and a useful crosssection area of 40 cm. the lamp being an elongated high pressure mercury vapor lamp of a 700 W. power.

There is circulated therethrough a mixture of hexane with carbon tetrachloride having a hexane and a 5% carbon tetrachloride content, to which are added 1% by weight of nitrosyl chloride and 50 ccm. of 70% by weight sulfuric acid.

This mixture is circulated at an average linear velocity of 1 cm./sec., a Reynolds Number of about 1,800 and a temperature of 5 C.

The concentration of nitrosyl chloride is kept constant (1% by Weight) during the reaction.

After one hour, the sulfuric acid solution is withdrawn and neutralized at a temperature of 25 C. by means of ammonia. which is extracted with ether, dried and distilled under reduced pressure (B.P. 10 mm. Hg=82 C.). There are thus produced 35 g. of a viscous oil consisting of about 50% of propylethylketoxime and 50% of butylmethylketoxime.

The molar yields are of 76% with respect to nitrosyl chloride and 84% with respect to hexane.

Example 8 Example 7 is repeated, except that the average linear velocity is 10 cm./sec. and the Reynolds Number is 18,000. After one hour, 40 g. of the same oil as in Example 7 have been obtained. The molar yields remain unchanged.

Example 9 Example 7 is repeated, except that hexane is replaced by heptane.

There is obtained the oxime as a viscous oil 5 There is obtained 40 g. of an oil (B.P. 16 mm. Hg=l C.) which consists of about 20% of dipropylketoxime, 40% of ethylbutylketoxime and 40% of methylamylketoxime. The molar yield is 74% with respect to nitrosyl chloride and 85% with respect to heptane.

Example 10 Example 9 is repeated, except that the average linear velocity is 10 cm./sec. and the Reynolds Number is 18,000.

After one hour, 46 g. of the same oil as in Example 9 have been obtained. The molar yields are the same as in Example 9.

Example 11 Example 12 Example 11 is repeated, except that the average linear velocity is 1-0 cm./ sec. and the Reynolds Number is 13,000.

The amount of cyclododecanone-oxime obtained in one hour is 47 g., the molar yields being unchanged.

From the foregoing description one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. Consequently, such changes and modifications are properly, equitably, and intended to be, within the full range of equivalence of the following claims.

What is claimed as this invention is:

1. A process for the production of a product selected from the group of oximes and salts thereof by nitrosation of a hydrocarbon selected from the group of alkanes and cycloalkanes, containing at least carbon atoms in the molecule, comprising the steps of:

(a) passing said hydrocarbon in liquid phase having dissolved therein a nitrosation agent in an amount less than 5% by weight, in front of an actinic light source at an average linear velocity of the liquid phase of at least 1 cm. per second and at a Reynolds Number, with respect to the reaction mixture, which is of the order of 5,000 to 50,000, and

(b) separating the formed reaction product.

2. A process for the production of a product selected from the group of oximes and salts thereof by nitrosation of a hydrocarbon selected from the group of alkanes and cycloalkanes containing at least 5 carbon atoms in their molecule, comprising the steps of:

(a) passing said hydrocarbon in liquid phase having dissolved therein a nitrosation agent in an amount less than 5% by weight, in front of an actinic light source at an average linear velocity of the reaction mixture of at least 1 cm. per sec-0nd, and at a Reynolds Number, with respect to the reaction mixture, which is of the order of 5,000 to 50,000;

(b) contacting the resulting reaction mixture With an aqueous solution of a strong mineral acid, at least substantially outside of the irradiation zone;

(c) separating the hydrocarbon phase from the phase of the strong mineral acid containing the formed reaction product; and

(d) recycling the hydrocarbon phase to the inlet of the reaction zone in admixture with fresh reactants.

3. A process according to claim 2 wherein the average linear velocity of the reaction mixture through the reaction zone is of at least 3 cm. per second.

4. A process according to claim 2 wherein said strong mineral acid is an aqueous selected from the group consisting of 5090% by weight sulfuric acid, 5090% by weight phosphoric acid, and concentrated aqueous hydrochloric acid.

5. A process for the production of a product selected from the group of oximes and salts thereof by nitrosation of a hydrocarbon selected from the group of alkanes and cycloalkanes containing at least 5 carbon atoms in their molecule, comprising the steps of:

(a) passing said hydrocarbon in liquid phase having dissolved thereinto a nitrosation agent in an amount less than 5% by weight, and maintained at a temp- .perature within the range of from 10 C. to 40 (3;, along an actinic light-transmitting surface at an average linear velocity of the reaction mixture of at least 1 cm. per second and at 11 Reynolds Number in the range of 5,000 to 50,000, and

(b) separating the formed reaction product.

6. A process for the production of a product selected from the group of oximes and salts thereof by nitrosation of a hydrocarbon selected from the group of alkanes and cycloalkanes containing at least 5 carbon atoms in their molecule, comprising the steps of:

(a) passing a mixture of said hydrocarbon with a nitrosation agent having less than a 5% content by Weight of the latter, and dissolved in a solvent therefor which is substantially inert with respect to said nitrosation agent, in front of an actinic light source at an average linear velocity of the solution of at least 1 cm. per second and at a Reynolds Number, with respect to the reaction mixture, which is of the order of 5,000 to 50,000, and

(b) separating the formed reaction product.

7. A process according to claim 6 wherein said solvent is benzene.

8. A process for manufacturing a product selected from the group consisting of cyclohexanone-oxime and salts thereof by nitrosation of cyclohexane, comprising the steps of:

(a) passing said cyclohexane in liquid phase having dissolved therein a nitrosation agent in an amount less than 5% by weight, in front of an actinic light source at an average linear velocity of the reaction mixture of at least 1 cm. per second and at a Reynolds Number, with respect to the reaction mixture, which is of the order of 5,000 to 50,000, and

(b) separating the formed reaction product.

9. A process for the production of a product selected from the group of oximes and salts thereof by nitrosation of a hydrocarbon selected from the group of alkanes and cycloalkanes containing at least 5 carbon atoms in their molecule, comprising the steps of:

(a) passing said hydrocarbon in liquid phase containing less than 5% by weight of nitrosyl chloride in front of an actinic light source at an average linear velocity of the reaction mixture of at least 1 cm. per second and at a Reynolds Number, with respect to the reaction mixture, which is of the order of 5,000 to 50,000, and

(b) separating the formed reaction product.

10. A process for manufacturing a product selected from the group consisting of cyclohexanone-oxime and salts thereof by nitrosation of cyclohexane at a temperature of from l0 C. to 40 C., comprising the steps of:

(a) passing a liquid mixture containing less than 5% by weight solution of nitrosyl chloride in cyclohexane with benzene, in front of an actinic light source at an average linear velocity of at least 3 cm. per second and at a Reynolds Number, with respect to the reaction mixture, which is of the order of 5,000 to 50,000;

(b) contacting the resulting reaction mixture with an aqueous solution of 50-90% by weight sulfuric acid, at least substantially outside of the reaction zone;

(c) separating the hydrocarbon phase from the sulfuric acid phase which contains the formed reaction product; and

(d) recycling the hydrocarbon phase to the inlet of the reaction zone in admixture with fresh reactants.

11. In a process for the nitrosation of a hydrocarbon selected from the group consisting of alkanes and cycloalkanes containing at least 5 carbon atoms in their molecules, by passing said hydrocarbon in the liquid phase and containing dissolved therein less than 5% by Weight of a nitrosation catalyst, at a linear velocity of at least 1 cm. per second, and at a temperature of the order of -10 to 40 C., in front of a source of actinic light hav- References Cited by the Examiner UNITED STATES PATENTS 11/1962 Taylor 204-162 4/1965 Metzger et a1. 204-162 JOHN H. MACK, Primary Examiner.

HOWARD S. WILLIAMS, Examiner. 

1. A PROCESS FOR THE PRODUCTION OF A PRODUCT SELECTED FROM THE GROUP OF OXIMES AND SALTS THEREOF BY NITROSATION OF A HYDROCARBON SELECTED FROM THE GROUP OF ALKANES AND CYCLOALKANES, CONTAINING AT LEAST 5 CARBON ATOMS IN THE MOLECULE, COMPRISING THE STEPS OF: (A) PASSING SAID HYDROCARBON IN LIQUID PHASE HAVING DISSOLVED THEREIN A NITROSATION AGENT IN AN AMOUNT LESS THAN 5% BY WEIGHT, IN FRONT OF AN ACTINIC LIGHT SOURCE AT AN AVERAGE LINEAR VELOCITY OF THE LIQUID PHASE OF AT LEAST 1 CM. PER SECOND AND AT A REYNOLDS NUMBER, WITH RESPECT TO THE REACTION MIXTURE, WHICH IS OF THE ORDER OF 5,000 TO 50,000, AND (B) SEPARATING THE FORMED REACTION PRODUCT. 